Various air bag restraint systems have been proposed in which an access door is arranged behind a continuously formed outer skin or cover. In some cases the underside of the outer skin is perforated or weakened. As shown in U.S. Pat. Nos. 3,622,176 and 4,246,213 the weakened sections represent underlying depressions in the outer cover which show through as an outline of the underlying air bag assembly. Furthermore, such systems require that the outer cover be torn apart at the weakened seams. If the seams are irregular in form the opening force will vary and at times may tend to impede the release of an air bag.
In other arrangements, the cover assembly includes a separate cutting device that will pierce the outer skin. Examples of such separate devices are set-forth in U.S. Pat. No. 4,097,064 and copending U.S. applications Ser. No. 601,406 filed Oct. 22, 1990.
Other cover arrangements for air bag assemblies on the driver side steering wheel location are shown in U.S. Pat. Nos. 4,911,471 and 4,852,907 in which a layer of low density foam is reinforced by a layer of mesh. Such arrangements are configured for attachment to a base plate that is connected by a bracket to the steering column of a vehicle. There is no provision for a separate layer of rigid foam material that is arranged to underlie and fully back a separate cover layer so as to form the load bearing support for an interior trim product such as an instrument panel having a hidden door formed therein. Rather, the cover forms a door that is directly attached to the sides of the air bag container structure.
Other air bag cover assemblies are shown in U.S. Pat. Nos. 3,794,349; 4,120,516; 4,791,019; and 5,082,310. None of these patents show or suggest a air bag cover assembly having a hidden door in a larger interior trim product such as an instrument panel having a passenger side air bag assembly therein and wherein the load bearing support is a low density, rigid foam material located beneath an outer decorative layer and wherein the single load bearing support is formed of a low density material having a thickness and flexural modulus that in combination will produce a resultant door stiffness that will enable the hidden door to penetrate the outer decorative layer to form a deployment opening therethrough, e.g., the door has a stiffness great enough to fracture the materials defining the hidden tear seam.